[JIRAALIGN-1589] Release/PI: User are able to rename a release title with an existing one

Issue Summary

Users are able to modify a Release/PI title to an existing one.

Steps to Reproduce

1. Navigate to Release/Program Increment (Make sure you have several Release on the grid)
2. Select a particular release and edit the title to be same as another release on the grid.
   

Expected Results

User should not be able to rename a Release/PI if the title already exists.

Actual Results

User is able to rename the title to an existing one.

Workaround

None.